This invention relates to a golf club, and more particularly to a golf club, in which a shaft receiving bore in a club head extends into an opening in the lower surface of a sole plate, the club having an improved coupling strength between the club shaft and the club head as well as an improved manufacturing efficiency of and an improved processability of the materials of the golf club.
In a wood type golf club, distortion of the club head that occurs when a ball is driven therewith is lessened and the degree of pleasantness realized from the swing of the golf club as well as the degree of accuracy of direction of a ball driven therewith are increased, in proportion to the coupling strength of the club shaft with respect to the club head. In the past, to achieve the best coupling strength of a club shaft with respect to a club head, and with reference to FIG. 11, a shaft receiving bore 3 is provided in a club head 1 so that the bore 3 extends from the upper end of the hosel of the head into a sole plate 4 that has an opening in its lower surface. A club shaft 2 is then inserted into this bore 3 until the lower end of the club shaft 2 has reached the lower surface of the sole 4 and a bottom plug 6 is then fitted in the interior of the lower end portion of the club shaft 2 and fixed in this location. It has been accepted that a golf club in which the lower end of the club shaft 2 reaches the lower surface of the sole 4 has a high coupling strength and givers golfers a sense of security. The "high coupling strength of a golf shaft with respect to a sole" constitutes one of the conditions for advanced golfers' selecting a golf club.
When a club head 1 of a golf club in which the lower end of a club shaft 2 reaches the lower surface of a sole 4 is being manufactured, the club shaft 2 is typically inserted into a shaft receiving bore 3 so that it projects downwardly beyond the sole 4, the projecting end portion of the club shaft 2 then being cut off flush with the sole and the cut end of the club shaft polished. However, the presence of the upper portion of the club shaft 2 tends to interfere with this polishing operation and causes the productivity of the golf clubs to decrease greatly.
Golf clubs in which improvements have been made in view of such a low productivity problem include a golf club in which a club shaft 2 is inserted into a bore 3 so that its lower end thereof does not reach the lower surface of a sole 4, with a bottom plug 6 then being fitted from the lower side of the sole 4 in an opening portion 3a, which is in the sole 4, of the bore 3 as shown in FIG. 12. In the golf club of this construction, the club shaft 2 can be joined to a club head 1 after the club head 1 has been polished independently of the club shaft. Accordingly, polishing of the club head 1 is not obstructed by the club shaft 2, so that productivity of the golf club is higher.
Although the golf club shown in FIG. 12 has an excellent processability of the materials therefor and an excellent productivity, the length of the portion of the club shaft 2 which is inserted into the head body becomes shorter. Therefore, the area of the surfaces bonded together between the club shaft 2 and club head 1 decrease as compared with that of the corresponding surfaces in the golf club of FIG. 11, so that the coupling strength of the club shaft 2 with respect to the club head 1 becomes lower.
In order to regulate the weight of these golf clubs of FIGS. 11 and 12, weight balance regulating weights 8 are inserted as shown in FIGS. 13 and 14 respectively on the bottom plugs 6 which are fitted in the bore 3 as mentioned above.
However, it is very difficult to regulate the weight balance of such golf clubs by means of the weights 8 fitted in the interior of the shaft receiving bores 3. Especially, the golf club of FIG. 12 in which the club shaft 2 is inserted into the bore 3 so that the lower end of the club shaft 2 is located within the bore 3 and does not reach the sole 4, because here the length of the portion of the club shaft 2 which is inserted into the bore 3 has to be decreased by a distance corresponding to the total length of the bottom plug 6 and weight 8. Therefore, the area of the surfaces bonded together between club shaft 2 and club head 1 decrease even more causing yet a further decrease in the coupling strength of these parts.